Tomoko Hirayama 교수

To observe in situ the adsorption of fatty acid onto metal surfaces, cross-sectional images of the adsorption layer were acquired by frequency-modulation atomic force microscopy (FM-AFM). Hexadecane and palmitic acid were used as the base oil and typical fatty acid, respectively. A Cu-coated silicon wafer was prepared as the target substrate. The solvation structure formed by hexadecane molecules at the interface between the Cu substrate and the hexadecane was observed, and the layer pitch was f

Performances of an oil-lubricated spiral-grooved journal bearing are investigated in this paper with special attention paid to cavitation occurrence. The “equivalent flow model,” which is a theoretical scheme for taking the cavitation occurrence into hydrodynamic lubrication theory, is applied to the analyses by a finite difference treatment of the Reynolds equation that deals with the geometry of a finite number of grooves. The calculated results are compared with experimental results under ecc

Abstract Boundary lubrication is one of the most interesting topics in the field of tribology, and a lot of studies have been conducted from the past for understanding the behaviour of boundary lubrication films. General boundary lubrication films are formed by the adsorption of additives mixed into lubricant, and then the tribological performances are drastically improved in many cases. However, there is still room for discussion on the “actual” behaviour of adsorbed additive layer in the tribo

The effects of nanotexturing on oil film thickness and shape under pointcontact elasto-hydrodynamic lubrication (EHL) conditions were experimentally investigated. A disk-onball friction tester with an optical interferometer was used to measure oil film thickness and to observe the oil film shape. Periodic groove structures with a spiral, perpendicular, or parallel shape and with various groove depths and distances were formed by irradiation of a femtosecond laser onto the surface of steel balls.

Abstract Boundary lubrication is one of the most interesting topics in the field of tribology, and many studies have been conducted in the past to gain deeper understanding of the behaviour of boundary lubrication layers formed by additives mixed in lubricants because the layer largely affects the tribological property of the target surface. With a strong demand to clarify the behaviour of boundary lubrication layers, several new approaches to in situ (=in lubricant) analysis have been proposed

Abstract The shear force of oil film containing an oiliness additive in a narrow gap was measured with a newly developed parallel‐disk viscometer supported by an aerostatic thrust bearing. To evaluate viscometer performance, the shear force of pure base oil was first measured using an oleophobic coated disk. Using the coated disk resulted in interfacial slip between the disk surface and oil, which significantly reduced the shear force compared with that when a noncoated disk was used. Next, the

Abstract A hydrodynamic bearing with non‐uniform herringbone grooves has been developed for use with high‐speed motor spindles. The grooves gradually become narrower, shallower and less straight (curved) towards the herringbone centre along axial direction, resulting in an increased pumping effect of the spiral grooves. The optimum dimensions of the grooves for increasing the critical bearing number were clarified theoretically, and bearings with non‐uniform herringbone grooves were found to inc

Spiral-grooved bearings have lately attracted considerable attentions as better substitutions for current ball bearings, especially in motor spindles of precision equipments such as hard disk drive systems. In this paper, optimum designs of the groove dimensions of the spiral-grooved journal bearings specialized for a reduction of amplitude of the operating repeatable run-out (RRO), which is a major characteristic to be considered for applications to precision equipments, are theoretically discu

Dynamic characteristics of an oil-lubricated spiral-grooved journal bearing are theoretically investigated in this paper with considering the effect of cavitation occurrence in the bearing clearance. The Reynolds equation by cooperating with a cavitation theory called ‘equivalent flow model’ as a formulation for cavitation occurrence is expanded by perturbation scheme with respect to the journal eccentricity, so that the dynamic bearing characteristics, such as bearing stiffnesses and damping co